In many hydraulic systems such as are used in process control applications and in various test operations, it becomes necessary to sense when a predetermined fluid pressure is reached in the system in order that the system may respond thereto. Typically, a mechanical pressure switch is incorporated in the system to sense when the predetermined pressure is reached and to give an indication signal thereof. In high pressure hydraulic systems, a transient pressure spike may occur as the result of the abrupt closing of a system valve. This phenomenon, commonly known as "water hammer", can momentarily actuate the mechanical pressure switch. Similar transients might result from severe system vibration impulses. Since such transients are not the true static operating pressure of the system, it is oftentimes desirable to suppress actuations of the pressure switch or in the associated indication signals caused by "water hammer" transients or transient vibration impulses.
In the prior art control systems, suppression of transient pressure spikes is usually accomplished by mechanical damping in the pressure switch sensor cavity or in the associated transmission system for the control signal. For example,
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In the foregoing prior art systems, it is difficult to adjust with accuracy to a predetermined damping time. Furthermore, the damping times are fixed for a change of the measurand in only one direction, i.e., either an increasing or decreasing measurand.